All chains shows 349696347, the big differences depend on estimate function. Like when you expect new machines will be plugged in, the difficulty is predicted higher than if you expect no new machines are added for the remaining 6 days

dot-bit had the best prediction, but the page is down atm. bit coin difficulty . com just grabbed the number from the now defunct dot-bit page, and the chart from sipa, and then puts a banner ad on it to make money from other people's work.

If you scroll down to the second chart you can see how their past predictions evolved and panned out, and although the axis is logarithmic, still pretty decent.Its current estimate is ~400M, but just like the previous change, its probably not taking in to account the full impact of the KnC massive shipping, so this is probably too conservative.

With 2.8 petra hash the diff. needs to be ~390 million for the block rate target.Only about 700 tera hash need for 500 million diff.

The difficulty change isnt based on the last hashrate, but on the average hashrate over the previous period. So it will take a lot more than 700TH . To get to 500M at the next change, the network would need to have averaged 3.5 PH over the period. Since it started around 2.4 PH and was flat for some days, it would need to end closer to 5PH.

With 2.8 petra hash the diff. needs to be ~390 million for the block rate target.Only about 700 tera hash need for 500 million diff.

The difficulty change isnt based on the last hashrate, but on the average hashrate over the previous period. So it will take a lot more than 700TH . To get to 500M at the next change, the network would need to have averaged 3.5 PH over the period. Since it started around 2.4 PH and was flat for some days, it would need to end closer to 5PH.

Yes, I know this. See "for the block rate target". Just stating that the hash rate is there for X Difficulty. It will probably take a least one more Diff. correction after this coming one to be closer to the real target.